Packers are commonly employed for isolating sections of a perforated well casing adjacent oil producing formations. By isolating sections of a well casing between hydrocarbon producing formations, other depleted formations can be separated therefrom. Packers are also utilized to isolate sections of well casings to enable injection of fluids into selected formations, while isolating other formations.
Currently available casing packers typically include a tubular section with an elastomeric boot disposed therearound so that when radially expanded, a seal is effected within the casing. A packer is thus effective to isolate a casing into separate sections. The packer itself is generally fixed within the casing by employing a number of toothed slip members which are wedged between the packer tubular section and the well casing. An upper and lower set of slips are generally utilized, one having teeth oriented to prevent downward movement of the packer, and the other having teeth oriented in another direction to prevent upward movement of the packer.
Well casing packers are constructed for setting, or otherwise being fixed in a well casing by various techniques. For example, certain packers, known as "wire-line packers", are set by way of an electric wire-line which extends from the packer apparatus to the surface. By energizing the wire-line, a power charge is ignited and the packer is tripped so that the slips engage the casing, thereby setting the packer. Because of the general construction of such type of packers, only a modest amount of equipment can be supported therefrom as the packer is lowered within the well bore. Normally, a wire-line packer can support about 2,500 pounds of equipment suspended therefrom.
Hydraulic packers are available which are set with the use of pressurized hydraulic fluid. Some types of hydraulic packers can even be released by pumping a different fluid pressure downhole to the packer assembly. The disadvantage with the wire-line and the hydraulic type of packers is that expensive surface equipment is required. Particularly, electric wire-line dispensing trucks and heavy duty hydraulic pumping equipment are required to operate these packer assemblies.
Permanent, mechanical or drillable packers are another type of packer equipment which are set and permanently fixed within a casing. The drillable packers require additional downhole apparatus for setting the slips within the casing, but can support several hundred thousand pounds of equipment therefrom.
It can be appreciated that the operation of packers must be extremely reliable, otherwise the retrieval thereof from a casing several thousand feet deep may be extremely time consuming and expensive. In setting a mechanical packer, a drill string is often utilized in the setting process and disconnected therefrom and removed from the well bore thereafter. When a packer is utilized in conjunction with a well casing cementing operation, it is imperative that the drill string be completely disconnected from the packer, otherwise the entire drill string would be fixed within the well bore when the cement sets.
Packers can also be utilized in conjunction with well bore liners for cementing an isolated part of a casing. However, a problem of great concern in such an operation is the withdrawal of the packer setting equipment before the cement sets. As noted, any delay in removing the packer setting equipment may result in its being fixed by the cement within the casing. As a result of the risk of inadvertently cementing the drill string equipment within a well bore, packers are not widely used, if at all, in conjunction with cementing operations.
From the foregoing, it can be seen that a need exists for improved packer setting apparatus which can reliably set a mechanical packer within a casing, and be quickly and reliably released therefrom. An associated need exists for a technique in which a packer can be set and released without resorting to surface equipment which otherwise would not be required. Yet another need exists for a technique for fixing a packer and a liner within a well bore to achieve an improved seal when the combination is cemented within the well bore.